1. Field of the Invention
The invention is directed to an improved fuel injection apparatus for an internal combustion engine.
2. Description of the Prior Art
A fuel injection apparatus of the type with which this invention is concerned is known from EP 0 987 431 A2. This fuel injection apparatus has a high-pressure fuel pump and a fuel injection valve connected to it for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston, which the engine sets into a stroke motion and which defines a pump working chamber. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve member, which controls at least one injection opening and which the pressure prevailing in the pressure chamber can move in the opening direction, counter to a closing force, in order to open the at least one injection opening. A first electrically actuated control valve is provided, which controls a connection between the pump working chamber and a relief chamber. A second electrically actuated control valve is also provided, which controls a connection between a control pressure chamber and a relief chamber. The pressure prevailing in the control pressure chamber acts on the injection valve member at least indirectly in a closing direction and the control pressure chamber is connected to the pump working chamber. For an injection of fuel, the first control valve is closed and the second control valve is opened so that high pressure cannot build up in the control pressure chamber and the fuel injection valve can open. When the second control valve is open, however, fuel drains out of the pump working chamber by means of the control pressure chamber, so that of the fuel quantity delivered by the pump piston, the fuel quantity available for injection is reduced and so is the pressure available for the injection. As a result, the efficiency of the fuel injection apparatus is less than optimal.
The fuel injection apparatus according to the invention has the advantage over the prior art that for the fuel injection, the second control valve can be closed so that no loss in fuel quantity and fuel pressure occurs during the injection, thus improving the efficiency of the fuel injection apparatus. By means of the throttle restriction, when the second control valve is open, the outflow of fuel into the relief chamber results in a pressure loss in one of the partial chambers of the control pressure chamber so that the control piston and by means of it, the injection valve member, has a greater force exerted on it in the closing direction than when the second control valve is closed, i.e. when at least approximately the same pressure prevails in both partial chambers.
Advantageous embodiments and modifications of the fuel injection apparatus according to the invention are disclosed. In a simple way, one embodiment makes it possible for less force to be exerted on the control piston in the closing direction when the second control valve is closed than when the second control valve is open. An advantageous configuration of the throttle restriction is also disclosed.